Transluminally implantable intravascular devices, such as stents or grafts, are initially mounted upon or within a delivery catheter and then crimped into a compact configuration of a relatively small diameter to facilitate insertion and transluminal advancement of the device into the desired lesion requiring treatment. Thereafter, such devices are radially expanded to a larger operative diameter either by removing a constraining layer thereby releasing the device or by inflating a balloon on which the device is crimped. When expanded the device serves to support the vessel against its tendency to reclose and may also serve as a matrix for releasing a medically active substance.
It will be appreciated that the term “stent” may be used herein below as a general and non-limiting example of a catheter-mounted intravascular device. Both self-expanding and balloon expandable stents are well known and widely available in a variety of designs and configurations.
Prior art catheter systems for stent delivery provided a restraining sheath as a retractable sheath overlying the stent. One problem that arises when mounting the stent on the catheter system as well as during retraction of the sheath is excessive friction and rubbing between the sheath and the stent that may complicate and sometimes render stent deployment impossible. In addition, stents are often coated with a special polymer, a drug, or a combination thereof. Excessive friction and rubbing between the stent and the constraining sheath may cause damage to the integrity of the coated surface material of the stent by the friction between the sheath and the external surface of the stent. Moreover, such friction tends to increase even more when using longer stents or stents with a narrower crimping profile. Accordingly, it is an object of the invention to minimize friction between the catheter and the stent during deployment.
Another problem in the art arises with stents having relatively low axial rigidity, where axial friction forces applied during deployment or mounting of the stent on the catheter system may shorten the stent. It is therefore advantageous to have a catheter system that minimizes axial friction forces applied to the stent during deployment and mounting.
Yet another problem known in the art is related to the size of the proximal portion or the handle of catheter systems of self-expandable stents. Deploying such stents requires pulling the constraining sheath backward in the proximal direction a length which equals at least the length of the stent. When using longer stents (i.e. 100 millimeters and more) this limitation becomes a disadvantage as it leads to relatively long handles with a bulky mechanical structure that may be uncomfortable to operate. It is therefore advantageous to have a catheter system with a relatively short handle.